Method and apparatus for multi-channel operation in wireless local area network system

ABSTRACT

Disclosed are a method and apparatus for multi-channel operation, performed by an access point (AP), in a WLAN system, the method includes: transmitting channel assignment information to a plurality of stations (STAs), in which the channel assignment information is for assigning at least one of a first channel and a second channel to each of the plurality of STAs; transmitting channel activity information to the plurality of STAs, in which the channel activity information is for indicating an activity duration where the AP transmit or receive a frame through each of the first channel and the second channel; and transmitting or receiving a frame through the first channel or the second channel on the basis of the channel activity information.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 14/307,413, filed on Jun. 17, 2014, which is a continuation ofU.S. patent application Ser. No. 13/576,203, filed on Sep. 13, 2012, theentire disclosure of each of which is hereby incorporated by referencefor all purposes as if fully set forth herein. U.S. patent applicationSer. No. 13/576,203 is a U.S. national stage of PCT InternationalApplication No. PCT/KR2010/007384, filed on Oct. 26, 2010, and claimsthe benefit of U.S. Provisional Application No. 61/300,032, filed onFeb. 1, 2010. The national stage application also claims the benefit ofKorean Patent Application No. 10-2010-0061283, filed on Jun. 28, 2010.

TECHNICAL FIELD

The present invention relates to a wireless local area network (WLAN)system, and more particularly, to a method and apparatus formulti-channel operation in a WLAN system.

BACKGROUND ART

There are frequency bands that can be shared by other kinds of wirelesscommunication systems, one of which is a television white space (TV WS).The TV WS is an idle frequency band remained as an analog TV becomesdigitalized, and this band corresponds to a spectrum of 54˜698 MHzassigned for TV broadcasting. If a licensed device having priority touse a relevant frequency domain does not use this frequency band, anunlicensed device can use this frequency band.

If the IEEE 802.11 is applied to the TV WS, there is an advantage thatcoverage is noticeably extended due to the spectrum characteristics ofthe TV WS. However, in general, if the coverage is extended, the numberof STAs within the coverage is definitely increased. As the number ofSTAs increases, a method for flexibly managing users, i.e., scalabilitybecomes an object of concern. Further, since various wirelesscommunication systems and various unlicensed devices coexist, a problemof coexistence occurs. If distributed coordination function (DCF) andenhanced distributed channel access (EDCA) protocols of IEEE 802.11 areapplied to this environment, the problem of scalability may grow worse.

The DCF is a channel access mechanism used in IEEE 802.11 and based oncarrier sense multiple access/collision avoidance (CSMA/CA). Also, theEDCA corresponds to a competition-based medium access method amongchannel access models proposed in a hybrid coordination function (HCF)provided by extension of a general medium access control protocol. TheHCF is a protocol provided by IEEE 802.11e proposed to guarantee qualityof service (QoS).

Further, if an IEEE 802.11 protocol is applied to the TV WS, it isexpected that overlapping base service sets (BSSs) are rapidlyincreased. For example, if a user voluntarily installs an access point(AP) supporting the TV WS, coverage of the AP is so large thatoverlapping zone may increase.

When trying to use the TV WS, an unlicensed equipment utilizesgeo-location database to acquire an available channel a correspondingzone. Also, to solve a problem of coexistence between unlicensedequipments, there is a need for a signaling protocol such as a commonbeacon frame or the like.

A terminal for the IEEE 802.11 TV WS refers to an unlicensed equipmentthat operates using IEEE 802.11 MAC and PHY in the TV WS. Hereinafter, astation (STA) and AP operating in the TV WS will be called a WS STA anda WS AP, respectively.

The WS STA has to provide a protection function for an incumbent user.That is, if the incumbent user such as a microphone is in of use, the WSSTA has to stop the use of a channel for protecting the incumbent user.To this end, the WS STA requires a spectrum sensing mechanism. Thespectrum sensing mechanism includes an energy detection method, asignature detecting method, etc. It is determined that the incumbentuser is in of use if strength of a received signal is equal to or higherthan a certain value, or it is determined that the incumbent user is inof use if a DTV preamble is detected. However, a WS communicationmechanism that reflects the incumbent user protection function of acommon WS may have troubles in maintaining quality of service andsecuring reliability since an ascertain and standby time is taken.Accordingly, a more-detailed WS communication mechanism is required tomaintain the quality of service and secure the reliability of the WSSTA.

SUMMARY OF INVENTION Technical Problem

The present invention provides a method and apparatus for multi-channeloperation of guaranteeing coexistence with other wireless communicationsystems, in a wireless local area network (WLAN) system.

Solution to Problem

In an aspect of the invention, there is provided a method formulti-channel operation, performed by an access point (AP), in awireless local area network (WLAN) system. The method includestransmitting channel assignment information to a plurality of stations(STAs), in which the channel assignment information is for assigning atleast one of a first channel and a second channel to each of theplurality of STAs; transmitting channel activity information to theplurality of STAs, in which the channel activity information is forindicating an activity duration where the AP transmit or receive a framethrough each of the first channel and the second channel; andtransmitting or receiving a frame through the first channel or thesecond channel on the basis of the channel activity information.

Each of the plurality of STAs may perform channel sensing for detectingwhether an incumbent user occupies the operation channel in a durationexcept the activity duration of an operation channel.

The channel activity information may include a channel indicator, anactivity offset indicating a point of time when the activity durationfirst starts for a channel indicated by the channel indicator, a lengthof the activity duration and an activity interval between the activitydurations.

The activity duration may periodically be set, and the channel activityinformation may further include a set cycle of the activity duration oreach interval between the set activity durations.

The channel assignment information and the channel activity informationmay be transmitted to the plurality of STAs through a probe responseframe.

The channel assignment information and the channel activity informationmay be transmitted through a beacon frame.

The AP may transmit the beacon frame through the first channel, and theSTA assigned with the second channel as an operation channel may switchto the first channel and receive the beacon frame through the firstchannel at a point of time when the beacon frame is transmitted.

The AP may transmit the beacon frame through the first channel, and maytransmit a multi-channel information element frame including the channelactivity information through the second channel.

The first channel and the second channel may be of a television whitespace (TV WS) band.

In another aspect of the invention, there is provided a wirelessapparatus. The wireless apparatus includes a radio frequency (RF) unitwhich transmits or receives a frame and a processor which operates whileoperably connecting with the RF unit.

The processor is set for transmitting channel assignment information toa plurality of stations (STAs), in which the channel assignmentinformation is for assigning at least one of a first channel and asecond channel to each of the plurality of STAs, transmitting channelactivity information to the plurality of STAs, in which the channelactivity information is for indicating an activity duration where the APtransmit or receive a frame through each of the first channel and thesecond channel and transmitting or receiving a frame through the firstchannel or the second channel on the basis of the channel activityinformation.

Advantageous Effects of Invention

In a WLAN system, there are provided a method and apparatus formulti-channel operation, so that efficiency of using a wireless mediumcan be improved to thereby improve a throughput of a WLAN system andreliability of data transmission.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows configuration of a wireless local area network (WLAN)system according to an exemplary embodiment of the present invention.

FIG. 2 shows an example of a frame transmitting/receiving method of aWLAN system using a channel of a TV WS band to transmit a frame.

FIG. 3 shows operation of a STA in a WLAN system using a WS bandaccording to an exemplary embodiment of the present invention.

FIG. 4 shows an example of a multi-channel information element formatfor transmitting multi-channel activity information.

FIG. 5 is a block diagram showing an example of a configuration of achannel activity information field.

FIG. 6 shows operation of a WS STA in each channel according to anexemplary embodiment of the present invention.

FIG. 7 shows an example of multi-channel operation and a transmissionmethod of the multi-channel information element in the WS AP accordingto another exemplary embodiment of the present invention.

FIG. 8 is a block diagram showing a structure of a wireless apparatus inwhich an exemplary embodiment of the present invention can be realized.

MODE FOR THE INVENTION

Below, exemplary embodiments of the present invention will be describedin detail with reference to accompanying drawings. To easily explain thepresent invention, a method for multi-channel operation in a wirelesslocal area network (WLAN) system using a band of a television whitespace (TV WS) and an apparatus supporting the same will be described byway of example. However, the scope of the present invention is notlimited thereto, and may be equally applied to a WLAN system operatingto be used for multi-channels.

FIG. 1 shows configuration of a wireless local area network (WLAN)system according to an exemplary embodiment of the present invention.

Referring to FIG. 1, the WLAN system includes one or more basic serviceset (BSS). The BSS is a group of stations (STA) which can successfullysynchronize and communicate with one another, and does not mean acertain zone.

An infrastructure BSS (BSS1, BSS2) includes one or more non-access point(AP) STAs (non-AP STA1, non-AP STA2, non-AP STA2); APs (AP STA1, APSTA2) providing distribution service; and a distribution system (DS)connecting the plurality of APs (AP STA1, AP STA2). In theinfrastructure BSS, the AP manages the non AP STAs.

On the other hand, an independent BSS (IBSS) is a BSS that operates inan Ad-Hoc mode. Since the IBSS does not include the AP, there is nocentralized management entity that performs centralized management. Thatis, in the IBSS, the non-AP STAs are managed in a distributed manner. Inthe IBSS, all STAs may be provided as mobile STAs and constitute aself-contained network since access to the DS is not allowed.

A station (STA) is a predetermined functional medium having a mediumaccess control (MAC) and a physical layer interface for a wirelessmedium, based on institute of electrical and electronics engineers(IEEE) 802.11 standards, which broadly includes both the AP and thenon-AP STA. Further, a station operable in a TV WS band (to be describedlater), i.e., employing this band as a communication channel will becalled a WS STA.

Among the stations, a potable terminal manipulated by a user is a non-APSTA: STA1, STA3, STA4 and STA 5, and simply a station may indicate anon-AP station. The non-AP STA may also differently called a terminal, awireless transmit/receive unit (WTRU), a user equipment (UE), a mobilestation (MS), a mobile terminal, a mobile subscriber unit, or the like.Further, a non-AP STA operable in the TV WS band is called a non-AP WSSTA or shortly called a WS STA.

Further, the AP (AP1, AP2) is a functional entity that provides accessto a distribution system (DS) via a wireless medium for the STAassociated with the corresponding AP. In the infrastructure BSSincluding the AP, communication between the non-AP STAs is basicallyperformed via the AP, but direct communication between the non-AP STAsmay be possible if a direct link is set.

The AP may be also called a central controller, a base station (BS), anode-B, a base transceiver system (BTS), a cite controller, or the like.Further, the AP operable in the TV WS band (to be described later) iscalled a WS AP.

The plurality of infrastructure BSSs may be connected to one anotherthrough the distribution system (DS). The plurality of BSSs connectedthrough the DS is called an extended service set (ESS). The STAsincluded in the ESS can communicate with one another, and the non-APSTAs within one ESS can move from one BSS to another BSS whileperforming the communication without disconnection.

The DS is a mechanism that enables one AP to communicate with anotherAP. Through the DS, the AP can transmit a frame for the STAs associatedwith the BS managed by the AP, transmit a frame when one STA moves toanother BSS, or transmit a frame to an external network such as a wirednetwork or the like. The DS is not necessarily a network, but may beachieved without any limitation as long as it can provide predetermineddistribution service based on IEEE 802.11. For example, the DS may be awireless network such as a mesh network, or a physical structureconnecting the APs with one another.

The WS STA using the TV WS band has to provide a protection function fora licensed user, the reason of which is because the licensed user haspriority in using the corresponding band. The licensed user indicates auser allowed to use the WS band, and may be also called a licenseddevice, an incumbent user, a primary user, a major user or the like.Hereinafter, these will be commonly called the incumbent user. In thecase of the incumbent user (e.g., DTV, microphone, etc.) is alreadyusing a certain channel of the WS band, the corresponding channel hasnot to be available in order to protect the incumbent user.

Therefore, to use a certain channel, the WS AP or the WS STA has topreviously undergo a procedure of determining whether the correspondingchannel is available, i.e., whether the incumbent user occupies thecorresponding channel. The determination of whether the incumbent useris using the corresponding channel, i.e., detection of a signal from theincumbent user occupying the corresponding channel is called spectrumsensing.

The WS AP and the WS STA can use the corresponding channel afterascertaining that the corresponding channel is unoccupied for at least30 seconds. In other words, it is possible to transmit a signal onlyafter waiting at least 30 seconds even though the channel is unoccupied.Further, the WS STA has to monitor the corresponding channel at leastonce every 60 seconds, and has to stop transmitting a signal through theuse channel within 2 seconds if the signal of the incumbent user issensed in the corresponding channel. A rule of the channel monitoring orinterference avoidance is not only applied to the WS STA but alsodirectly applied to the WS AP

FIG. 2 shows an example of a frame transmitting/receiving method of aWLAN system using a channel of a TV WS band to transmit a frame.

Before transmitting a signal, the WS STA or the WS AP trying to use achannel A 210 of the WS band ascertains whether the channel A 210 isidle or not through the spectrum sensing (S211). As a result of thespectrum sensing, if the channel A 210 is not occupied by the incumbentuser, i.e., if a signal of the incumbent user is not detected in thechannel A 210, the WS STA or the WS AP waits at least 30 seconds (S212).After the spectrum sensing and waiting at least 30 seconds, if thechannel A 210 is still unoccupied by the incumbent user, the WS STA orthe WS AP transmits/receives a frame through the corresponding channel(S213). Thereafter, the WS STA or the WS AP monitors every 60 secondswhether the signal of the incumbent user is sensed with regard to thechannel A 210.

As shown in the example of FIG. 2, if the signal of the incumbent useris sensed as a result of monitoring the channel after 60 seconds (S214),the WS STA or the WS AP stops transmitting/receiving the frame throughthe channel A 210 within 2 seconds. As the incumbent user occupies thechannel A 210, the WS STA or the WS AP that cannot use the channel A 210performs the spectrum sensing with regard to another channel B 220 inthe WS band (S221). Like the foregoing procedures for using the channelA 210, the WS STA or the WS AP can transmit/receive a frame (S223) onlyafter waiting 30 seconds (S222) even though it is ascertained that thechannel B 220 is idle.

Through the above method for providing the protection function withregard to the incumbent user, the WLAN system using the channel of theWS band has to switch the use channel in accordance with a change of achannel condition (e.g., an appearance of the incumbent user), and hasto perform sensing or the like with regard to a target channel everytime when the channel is switched. Accordingly, it is so difficult tocontinuously transmit/receive the frame that the throughput of the WLANsystem may be decreased, the reliability of the frame transmission maybe deteriorated, and quality of service may be noticeably lowered.

According to an exemplary embodiment of the present invention, the APsimultaneously operates a plurality of channels and keeps monitoringwhether the incumbent user appears in each of the plural channels. Ifthe incumbent user appears in one channel among the plural channels, theAP and the STA can switch to another channel kept being monitored. Atthis time, the AP and the STA can directly transmit/receive the framewithout any standby time due to the channel switching since it is beingcontinuously monitored whether the incumbent user exists in a targetchannel for the channel switching.

For instance, the TV WS band has a plurality of channels and assigns abandwidth of 6 MHz for each channel. Thus, the WS AP occupies andoperates a plurality of available channels, in which the operation isbased on priority given to the respective channels. In practice, onlyone channel is used for transmitting/receiving the frame, while theother channels undergo the spectrum sensing.

In the WLAN system using the TV WS band according to an exemplaryembodiment of the present invention, the frame can be transmittedto/received from the STA operating in each of the plural channelsthrough the plurality of channels. Below, a case of two channels will bedescribed for easily explaining the present invention, but not limitedthereto. Alternatively, the present invention may be equally applied toa case where three or more channels are used in transmitting/receivingthe frame.

FIG. 3 shows operation of a STA in a WLAN system using a WS bandaccording to an exemplary embodiment of the present invention.

A WS STA 305 receives a multi-channel activity message from a WS AP 300(S310), and receives an operation channel assignment message (S320).

If the WS AP 300 manages a first channel and a second channel,multi-channel activity information includes information about a periodof operating in the first channel and information about a period ofoperating in the second channel. The WS AP 300 can operate switchingbetween the first channel and the second channel. When the WS AP 300operates in the first channel, it can be stated that the first channelis active but the second channel is inactive. Likewise, when the WS AP300 operates in the second channel, it can be stated that the secondchannel is active but the first channel is inactive. That is, that acertain channel is active indicates that the WS AP operates in thecorresponding channel or that a frame exchange is possible between theWS AP and WS STA operating in the corresponding channel.

If a certain channel is inactive, it means that the WS AP does notoperate in the corresponding channel and thus the frame exchange isimpossible between the WS AP and the WS STA. During an inactive period,the WS STA may continuously monitor (sense) whether the incumbent userappears in the corresponding channel.

In this exemplary embodiment, an activity duration and an inactivityduration of a certain channel may be respectively represented as a frameexchange period and a channel sensing duration in light of operationperformed by the WS STA in the respective durations.

Information about the activity/inactivity durations of each channel,determined by the WS AP 310 and transferred to the STA, may be formedbased on a regional location of the WS AP 310. The WS AP 310 can knowinformation such as a location of a TV broadcasting stationcorresponding to the incumbent user, a use pattern, etc. through database (DB) in advance. Therefore, the WS AP 310 can select a plurality ofchannels to operate by using the information of the DB, and determinethe activity/inactivity durations of the channels, thereby informing theWS STA 305 of that.

In FIG. 3, the operation channel assignment message includes informationabout the channel that the WS STA 305 will operate. The WS AP 300 maygroup the STAs associated with the WS AP 300 and assign the channel,where the STA will operate, to the STA, which belongs to the STA group,with regard to each STA group.

The multi-channel activity information and the operation channelassignment information of FIG. 3 may be transmitted to the STA 305through individual frames, respectively, or transmitted as beingincluded in one frame.

The STA 305 that receives the multi-channel activity message and theoperation channel assignment message ascertains information about anoperation channel assigned thereto, included in the operation channelassignment message, and switches to the operation channel assignedthereto (S330).

Then, the STA 305 acquires the activity information of the operationchannel, where it operates, from the multi-channel activity message, andtransmits/receives the frame in the activity duration while performingthe spectrum sensing to sense whether the incumbent user using theassigned channel exists in the inactivity duration with respect to thechannel where the STA 305 operates (S340).

FIG. 4 shows an example of a multi-channel information element formatfor transmitting multi-channel activity information.

A multi-channel information element 400 includes an element identifier(ID) 410, a length 420, the first channel activity information 430, andthe second channel activity information 440.

The element ID field 410 functions as an identifier of the correspondinginformation element, and the length field 420 indicates the length ofthe multi-channel information element 400. FIG. 4 shows just an examplethat two channels, the first channel and the second channel, are underoperation. If three or more channels are under operation, channelactivity information fields may be added as many as the number ofoperation channels. In FIG. 4, the length of each field is nothing butan example, which may be varied depending on the sizes of differentinformation added to the corresponding field.

The STA receives a frame containing a multi-channel information element,and exchanges the frame with the AP in the activity duration of thechannel by referring to the activity information field of the channelcorresponding to the operation channel assigned thereto in themulti-channel information element, thereby sensing the operation channelin the inactivity duration.

FIG. 5 is a block diagram showing an example of a configuration of achannel activity information field.

The channel activity information 430 includes a channel number 431, anactivity offset 432, an activity duration 433 and an activity interval434. The channel number 431 is used for distinguishing which channel thechannel activity information 430 relates to, and the activity offset 432indicates a point of time when the first activity duration of thecorresponding channel starts. The activity duration 433 indicates alength of time corresponding to the first activity duration of thecorresponding channel, and the activity interval 434 indicates aninterval between the activity durations, i.e., a value corresponding tothe inactivity duration.

The WS STA acquires the activity information of the first and secondchannels through the multi-channel information element 400 transmittedas being included in a probe request frame or a beacon frame. In thecase of the first channel, it is possible to grasp which channel thechannel activity information relates to on the basis of the channelnumber 431 included in the first channel activity information 430.Further, it is possible to start transmitting/receiving the frame of thecorresponding channel by grasping a start time of the active period onthe basis of the activity offset 432. Then, the frame istransmitted/received during a period indicated by the activity duration433, and if the active period is terminated, channel sensing isperformed by recognizing the inactivity duration up to a point of timeindicated by the activity interval 434.

According to an exemplary embodiment of the present invention, thechannel activity information may be transmitted as being included in aprobe response frame transmitted from the WS AP to the WS STA inresponse to a probe request frame transmitted for scanning the neighborBSS at an early stage that the WS STA accesses a network. Also, thechannel activity information may be transmitted as being included in abeacon frame if there is a need for transmitting the channel activityinformation again as the activity information is changed duringcommunication. At this time, the probe response frame or the beaconframe may contain the multi-channel information element of FIG. 4.

The beacon frame is a frame periodically transmitted by the WS AP, whichcan carry changed activity information if the activity information ofthe channel is changed. That is, the WS AP may transmit the changedchannel activity information to the WS STA as being included in thebeacon frame only if the channel activity information is changed, or mayperiodically transmit the latest channel activity information as beingincluded in the beacon frame.

According to an exemplary embodiment of the present invention, the WS APmay transmit only the channel activity information about the channelassigned to the corresponding WS STA, but may transmit the channelactivity information about unassigned channels for quick channelswitching when sensing the signal of the incumbent user. A plurality ofchannel activity information is transmitted at once as being included inthe multi-channel information element and the channel activityinformation may include various information such as a channel number, anactivity duration, etc.

FIG. 6 shows operation of a WS STA in each channel according to anexemplary embodiment of the present invention.

The frame is transmitted/received through the assigned channel and apoint of time to practically perform the communication and the spectrumsensing is based on information about the activity/inactivity durationincluded in the channel activity information.

The WS STA1 610 assigned with the channel A transmits/receives the framein the activity duration, but senses the assigned channel A in theinactivity duration. Similarly, the WS STA2 650 assigned with thechannel B senses the assigned channel B in the inactivity duration, buttransmits/receives the frame in the activity duration. At this time,sensing the assigned channel is detecting whether the incumbent userexists (or appears) in the corresponding channel. The WS AP and the WSSTA stops occupying the corresponding channel when sensing the signal ofthe incumbent user in the channel corresponding to the activityduration, and switches the use channel into the corresponding channel ofthe inactivity duration, thereby transmitting/receiving the frame.

According to an exemplary embodiment of the present invention, the framecan be transmitted/received between the WS AP and the WS STA in theactivity duration of each assigned channel. However, a management framesuch as the beacon frame is transmitted through the primary channelamong the plurality of assigned channels. The primary channel is achannel for transmitting the management frames such as the beacon framefrom the WS AP. Therefore, the WS STA assigned with the primary channelamong the plurality of WS STAs can receive the beacon frameperiodically, but the WS STA assigned with other channels (hereinafter,referred to as a ‘secondary channel’) may not receive the beacon frame.However, because the multi-channel activity information and theoperation channel assignment information can be transmitted through thebeacon frame, the STAs operating in the secondary channel also have toreceive the beacon frame by regarding the secondary channel as theoperation channel.

To this end, the WS STA operating in the secondary channel receives thebeacon frame through the primary channel at a point of time when thebeacon frame is transmitted, and switches to the secondary channel,where it operated, after completely receiving the beacon frame, therebytransmitting/receiving the frame through its operation channel andperforming the spectrum sensing.

FIG. 7 shows an example of multi-channel operation and a transmissionmethod of the multi-channel information element in the WS AP accordingto another exemplary embodiment of the present invention.

The WS STA assigned with the secondary channel may receive the changedchannel activity information of the WS AP through the secondary channel.The WS STA1 710 can periodically receive the beacon frame 720 at beaconframe intervals 730 since it is assigned with the primary channel, andreceive the changed information when the channel activity information ischanged. On the other hand, the WS STA2 750 cannot receive the beaconframe 720 since it is assigned with the secondary channel. Therefore, toenable the WS STA operating in the secondary channel to receive thechanged channel activity information, the WS AP separately transmitsmulti-channel information element frame 760 containing the channelactivity information. In this case, the multi-channel informationelement frame 760 may contain the foregoing multi-channel informationelement of FIGS. 4 and 5. The WS STA2 750 employing the secondarychannel as the operation channel can acquire the channel activityinformation by receiving the multi-channel information element frame760. In the case of switching the channel (from the primary channel tothe secondary channel or from the secondary channel to the primarychannel), the WS AP may perform the spectrum sensing for a predeterminedperiod before transmitting/receiving the signal through the switchedchannel.

According to an alternative exemplary embodiment of the presentinvention, the AP may assign both the primary channel and the secondarychannel as the operation channels to a certain WS STA. In this case, theSTA assigned with both the primary channel and the secondary channel asthe operation channel can communicate the frame with the AP by switchingto the active channel on the basis of the activity information of eachchannel.

According to the quality of service (QoS) in the WS STA, for example ifthe corresponding WS STA requires service vulnerable to delay, such astransmission of voice data, the WS AP assigns both the primary channeland the secondary channel as the operation channel for this WS STA.Thus, the WS STA can transmit/receive the frame through the primarychannel in the duration where the WS AP operates in the primary channel(activity duration of the primary channel), and transmit/receive theframe through the secondary channel in the duration where the WS APoperates in the secondary channel (activity duration of the secondarychannel)

FIG. 8 is a block diagram showing a structure of a wireless apparatus inwhich an exemplary embodiment of the present invention can be realized.

Referring to FIG. 8, a wireless apparatus 800 includes a radio frequency(RF) unit 810 and a processor 820. The RF unit 810 receives a frame froman STA accessing an AP 800 and transmits it to the processor 820, andtransmits a frame received from the processor 820. The processor 820 isoperably connected with the RF unit 810 and is set to generate channelassignment information and channel activity information and transmit theinformation through the RF unit 810 on the basis of the channel activityinformation.

The processor 820 and/or the RF unit 810 may includeapplication-specific integrated circuit (ASIC), other chipsets, a logiccircuit and/or a data processor. A memory 620 may include a read-onlymemory (ROM), a random access memory (RAM), a flash memory, a memorycard, a storage medium, and/or other storage devices. If the exemplaryembodiment is realized by software, the foregoing method may be achievedby a module (procedure, function, etc.) for performing the foregoingfunctions. The module may be stored in a memory (not shown), andexecuted by the processor 820. The memory may be internally orexternally provided in the processor 820, and connected to the processor820 by a well-known means.

While the present invention has been particularly shown and describedwith reference to exemplary embodiments thereof, it will be understoodby those skilled in the art that various changes in form and details maybe made therein without departing from the spirit and scope of theinvention as defined by the appended claims. The exemplary embodimentsshould be considered in descriptive sense only and not for purposes oflimitation. Therefore, the scope of the invention is defined not by thedetailed description of the invention but by the appended claims, andall differences within the scope will be construed as being included inthe present invention.

The invention claimed is:
 1. A method for a station (STA) operating in awireless local area network (WLAN) system, the method comprising:receiving a beacon frame including operating channel information andchannel activity information from an access point (AP), the operatingchannel information indicating at least one operation channel, thechannel activity information indicating an activity duration duringwhich the STA can transmit a frame to the AP; and transmitting a frameto the AP based on the channel activity information, wherein the channelactivity information includes: one or more fields for indicating theactivity duration, and a channel indication field including informationfor distinguishing a primary channel from a secondary channel during theactivity duration, and wherein the one or more fields includes: anactivity offset field indicating a point of time when a first period ofthe activity duration starts, a length field indicating a length of eachperiod of the activity duration, and an interval field indicating aninterval between each period of the activity duration.
 2. The method ofclaim 1, wherein the STA receives a management frame only through theprimary channel.
 3. The method of claim 1, wherein the operating channelinformation indicates more than one operating channel.
 4. A station(STA) operating in a wireless local area network (WLAN) system, the STAcomprising: a radio frequency (RF) unit configured to receive a beaconframe including operating channel information and channel activityinformation from an access point (AP), the operating channel informationindicating at least one operation channel, the channel activityinformation indicating an activity duration during which the STA cantransmit a frame to the AP, the channel activity information including:one or more fields for indicating the activity duration; and a channelindication field having information to distinguish a primary channelfrom a secondary channel during the activity duration; and a processoroperably connected to the RF unit and configured to control the RF unitto transmit a frame to the AP based on the channel activity information,wherein the one or more fields includes: an activity offset fieldindicating a point of time when a first period of the activity durationstarts, a length field indicating a length of each period of theactivity duration, and an interval field indicating an interval betweeneach period of the activity duration.
 5. The STA of claim 4, wherein theRF unit is further configured to receive a management frame only throughthe primary channel.
 6. The STA of claim 4, wherein the operatingchannel information indicates more than one operating channel.